Nanotechnology Spotlight

First demonstration of a memristive nanodevice based on protein

(Nanowerk Spotlight) Memristors – the fourth fundamental two-terminal circuit element following the resistor, the capacitor, and the inductor – have attracted intensive attention owing to their potential applications for instance in nanoelectronic memories, computer logic, or neuromorphic computer architectures. R. Stanley Williams and his group at Hewlett Packard were the first to demonstrate a solid-state memristive device based on a titanium dioxide thin film, which was inserted between two platinum electrodes (see "Researchers map out the switching location of a memristor" with a video where Williams explains how a memristor works).

Scientists have been able to show that various materials such as metal oxides, chalcogenides, amorphous silicon, carbon, and polymer-nanoparticle composite materials exhibit memristive phenomena. One unanswered question so far has been whether natural biomaterials like proteins can be used for the fabrication of solid-state devices with transport junctions.

Researchers in Singapore have now demonstrated that proteins indeed can be used to fabricate bipolar memristive nanodevices. This work provides direct proof that natural biomaterials, especially redox proteins, could be
used to fabricate solid-state devices with transport junctions and can be the core component in the development of bioelectronic devices.

a,b) Scanning electron microscope (SEM) images of a device prepared with an OWL-fabricated nanowire with a ∼12 nm gap. c) A diagram of ferritin molecules spanning the ∼12 nm gap. d) The reaction scheme for the chemical immobilization of ferritin onto the sides of the gap. (Reprinted with permission from Wiley-VCH Verlag)

"Previous work on memristors were based on man-made inorganic/organic materials, so we asked the question whether it is possible to demonstrate memristors based on natural materials," Xiaodong Chen, an assistant professor in the School of Materials Science & Engineering at Nanyang University, tells Nanowerk. "Many activities in life exhibit memory behavior and substantial research has focused on biomolecules serving as computing elements, hence, natural biomaterials may have potential to be exploited as electronic memristors."

In a paper in the September 5, 2011 online edition of Small ("Protein-Based Memristive Nanodevices"), Chen and his team report a bipolar memristive nanodevice based on protein for the first time.

The researchers based their device fabrication on the chemical immobilization of ferritin molecules – a ubiquitous intracellular protein that stores iron – within on-wire lithography (OWL) generated nanogaps.

"The programmable resistive switches were due to the electrochemical processes in the active centre of ferritin" explains Chen. "In addition, we demonstrated that such ferritin-based nanodevices with reversible resistance can be used for nonvolatile memory based on write-read-erase cycle tests."

This work provides a direct proof that natural biomaterials, especially redox proteins, could be used to fabricate solid state devices with transport junctions, which have potential applications in functional nanocircuits.

As Chen notes, the researchers chose ferritin as a model system in this experiment for a variety of reasons: it is the main intracellular iron storage protein with a nearly spherical shell and an active mineral core of hydrous ferric oxide; ferritin exhibits high stability and can withstand a pH range of 2.0-12.0 as well as temperatures up to 80 °C, thus it is a desirable, natural biomaterial for fabricating electronic devices; the conductivity of ferritin has been measured by conductive AFM, highlighting the potential application of this protein in electronics; and the mechanism of iron uptake and release in vivo shows biological 'memory' storage, which provides a potential target to develop biomolecule-based memristors.

"Based on this work we will further explore the use of bio-integrated nanodevices in terms of fundamental challenges and potential applications," says Chen. "We also want to know how multifunctionality could be integrated into these nanodevices. However, we should also note that natural biomaterials such as DNA or proteins are not as stable as commonly used inorganic materials. Bio-inspired approaches may help us to resolve this problem."